1. Field of the Invention
The present invention relates to an apparatus for removing a coating from a coated synthetic resin product such as, for instance, a bumper or a side molding which is used as decoration for an automobile or a functional part serving as a buffer, or a CD-ROM or the like.
2. Description of the Related Arts
In recent years, due to rising interest in environmental problems and reuse of resources, the recycling of synthetic resin products has been advocated. For instance, in the automobile industry, attention is being given to the recycling of unusable products produced in the manufacturing process of resin products such as bumpers and side moldings, or the recycling of resin products removed and recovered from scrapped vehicles.
These kinds of resin products such as bumpers and side moldings are often coated in order to improve their external appearance and quality. For instance, in the case of a typical bumper, a film is coated on a resin material consisting of a thermoplastic resin such as a polypropylene resin, via a primer layer of a thermoplastic resin such as a chlorinated polyolefine resin. This coating is a thermosetting resin such as an amino-polyester resin, an amino acrylic resin, a polyester urethane resin or an acrylic urethane resin. Although these resins are liquid prior to curing, a cross-linking structure is formed therein by a baking finish process. Since this structure is strong and hard, the coated resin bumper has superior chemical resistance, heat resistance, abrasion resistance, weather resistance and surface glossiness.
However, when this coated bumper is directly crushed for reuse, the polypropylene resin material serving as the base material of the resin product becomes contaminated with coating pieces. When such a polypropylene resin material contaminated with the coating pieces is molded, the fluidity of the molten resin is inhibited by the presence of the coating pieces, with the result that molding defects such as "burning", "weld marks" and "air bubbles" may occur in the resin product, and the coating pieces rising to the surface of the resin product may spoil the external appearance of the resin product.
Furthermore, although the coating pieces are thermosetting resin, the polypropylene resin serving as a base resin is a thermoplastic resin. Therefore, there is no appreciable interaction between the coating pieces and the base resin, so that kneading of the regenerated recycled resin is inhibited by the coating pieces which have not been minutely dispersed, with the consequence that the mechanical property of the recycled resin product notably deteriorates and the application range of the recycle resin product is greatly restricted.
It is therefore necessary to remove the coating when recycling the coated resin product. An apparatus for removing a coating from a resin product is disclosed in Japanese Patent Laid-Open No. 5-337941, which proposes a removing apparatus for the surface of a synthetic resin product as illustrated in FIG. 16.
In this removing apparatus, a resin product, such as a side molding 102, is carried by a pair of conveying rollers 101 between rolls 103 and 104 which are made from a synthetic resin foam. The carrying speed V of the side molding 102 is set to be lower than the rotational peripheral speed of the rolls 103 and 104 so as to apply cutting and high frictional forces to a coating 102a and a double face adhesive tape 102b on the surfaces of the side molding 102, thereby cutting and removing the coating 102a and the pressure sensitive double face adhesive tape 102b. The side molding 102 is thus delivered outside the system by means of the pair of conveying rollers 101.
However, in this apparatus, a resin product is brought into contact with rolls 103 and 104 which are made of a foamed resin, so that the rolls 103 and 104 are subject to brittle fracture which may generate dust and worsen the working environment. Furthermore, this apparatus is unsuitable for use with bent or curved resin products.
A countermeasure against these problems is disclosed in Japanese Patent Laid-Open Publication No. 7-25664, which illustrates a method for removing a coating from resin material, wherein a resin body having a coating thereon is rolled through a coat removing apparatus, comprising a pair of rolls rotating at different peripheral speeds which are provided facing the coated resin body, and a shear stress is applied between the resin material and the coating thereby removing the coating from the resin material.
In the case of this apparatus, a resin body is rolled between rolls having different peripheral speeds which are provided facing the resin body, and a shear stress is applied to the interface between the resin body and the coating thereby removing and removing the coating from the resin material. For this reason the coating removal rate is high. Furthermore, there is no toxicity since no solvents or the like need be used, and consequently this method has superior environmental safety.
However, when the resin bodies from which coating is to be removed differ in thickness, the size of the gap between the rolls must be adjusted in accordance with the thickness of the resin bodies in order to apply a suitable shear stress to the resin material. Furthermore, when the parts of the same resin body have different thickness, it is difficult to apply a uniform shear stress to the entire surface of the coating, which is likely to reduce coating removal efficiency.